OzVMX Forum

Marque Remarks => Yamaha => Topic started by: IT400C on April 29, 2010, 01:35:01 pm

Title: YZ400C Jetting
Post by: IT400C on April 29, 2010, 01:35:01 pm

Hi Guys,

What's the standard jetting for a YZ400C?  I'm doing a Replica ISDT IT400C, and the factory bikes ran a YZ400C silencer with standard YZ400C jetting.  I know with the vagueries of climate/engine condition/pipe and silencer condition, this probably wont be perfect, but it'll be a good starting point.

Thanks, Tony

Title: Re: YZ400C Jetting
Post by: mainline on April 29, 2010, 05:49:09 pm

According to the service data sheet

38mm Mikuni

Main Jet / Pilot Jet - 370 / 60
Needle Jet / Jet Needle-Clip position - Q-0 / 6F16-3
Slide Cutaway  - 3.0
Float Level - 18mm
Mixture screw - 1 1/2 turns out

Title: Re: YZ400C Jetting
Post by: IT400C on April 29, 2010, 10:58:07 pm

Compared to the IT400C (same motor, different silencer)

38mm Mikuni (VM38SS)

Main Jet / Pilot Jet - 340 / 60
Needle Jet / Jet Needle-Clip position - P-4 / 6F16-3
Slide Cutaway  - 3.0
Float Level - 18mm
Mixture screw - 1 turn out

Title: Re: YZ400C Jetting
Post by: IT400C on April 29, 2010, 11:34:05 pm

When they went to the YZ silencer and jetting on the ISDT bikes, they got an instant 3 1/2 horsepower more (measured), much improved mid-range power, and surprisingly, improved fuel economy....